1. Field of the Invention
This invention relates to the field of analysis and classification of marine animal sounds sensed by an array of hydrophones towed behind a ship and displayed electronically in conjunction with catalogued characteristics of sounds. The sounds can be predetermined or catalogued and used, as known sounds, to identify newly detected sounds. In particular, the invention enables the specific sounds of various species of marine animals to be detected and classified as to type and location.
2. Prior Art
Linear hydrophone arrays which are towed by ships to detect various type of marine sounds have been extensively used in the past. Such arrays have been used for offshore oil exploration to pick up and analyze sounds produced by the detonation of explosives or the use of other sound sources such as compressed air guns under water in order to explore the possibility that the sea bed contains sources of oil. Hydrophone arrays have also been used by naval antisubmarine forces to detect the sounds of submerged submarines. In addition, such arrays have been used by various oceanographic research groups to conduct studies of underwater sound propagation.
An early form of sound detector is described in U.S. Pat. No. 1,584,613 by Comstock et al, issued on May 11, 1926. In their device, microphones are spaced along a cable to be towed behind a ship. The spacing between adjacent microphones was proposed to be one-half the wavelength of the sound to be detected which would result in there being relatively few microphones or an extremely long cable in order to detect low frequency sounds. The signals are combined cumulatively. The array is most sensitive to sounds arriving in a broadside direction and least sensitive to sounds arriving from fore and aft directions. It is also proposed that the selectivity can be increased by incorporating tuned or resonating circuits between the microphones and indicating devices.
U.S. Pat. No. 3,239,803 of Godbey which issued on Mar. 8, 1966 describes another form of detection apparatus using a plurality of sound transducers spaced along a cable and connected together. Electrical signals from the transducers are amplified and passed through discriminating circuits arranged to identify the signals from each individual transducer. The output signals of the discriminators are recorded in a conventional manner.
U.S. Pat. No. 3,893,063 of Park et al. which issued on July 1, 1975, discloses a torpedo detection streamer comprising a plurality of microphone units which are maintained in a predetermined position to obtain a vertically oriented response pattern.
An elastic detection streamer device is described in U.S. Pat. No. 3,319,734 of Pavey which issued on May 16, 1967. In that device, the vibrations from the cable used to tow the sound detecting apparatus are absorbed by an elongated flexible mechanical vibration attenuator interposed between the forward end of the detection streamer and the trailing end of the towing cable. The vibration attenuator is in the form of an oil-filled flexible elastic tube generally similar to the detection streamer tubing and provided with conductors for carrying signals from the detection streamer to leads within the towing cable. A plurality of strain cables of a suitable elastic material, such as nylon, extend through the vibration attenuator to provide an elastic towing connection between the tow cable and the detection streamer. Both the vibration attenuator and the detection streamer contain oil to provide proper buoyancy at a predetermined submerged level. A line is connected to the aft end of the streamer and secured to a float or marker to make it possible to keep track of the location of the submerged streamer.